SMOBC in PCB stands for Soldermask Over Bare Copper, a printed circuit board (PCB) fabrication technique where the final metal layer is copper with no other protective metal plating. This means the copper is exposed and then covered by the soldermask, leaving only the component terminal areas uncovered for soldering.
Key Aspects of SMOBC:
- Bare Copper: The crucial characteristic is the final copper layer, which is left without any additional metallic coating, such as tin or gold.
- Soldermask Application: A layer of soldermask is applied directly over the bare copper, defining the areas where components will be soldered.
- Component Terminal Exposure: The soldermask is selectively applied, leaving pads and vias exposed for component placement and soldering.
Advantages of Using SMOBC:
- Cost-Effective: Eliminating the need for additional metal plating processes reduces manufacturing costs.
- Improved Solderability: Soldering directly to copper can, in some cases, provide excellent solder joints, provided the copper is properly prepared and protected.
- Planarity: SMOBC allows for a flatter surface compared to PCBs with plated finishes, which can be advantageous for fine-pitch components.
Disadvantages and Considerations:
- Copper Oxidation: Bare copper is susceptible to oxidation, which can impact solderability over time. Proper handling and storage are crucial. OSP (Organic Solderability Preservative) is often applied to address this.
- Need for Surface Treatment: To prevent oxidation and enhance solderability, bare copper PCBs often require surface treatment such as OSP (Organic Solderability Preservative).
- Shelf Life: Bare copper PCBs generally have a shorter shelf life compared to PCBs with plated finishes, due to the risk of oxidation.
In summary:
SMOBC is a cost-effective PCB fabrication method where the final copper layer is directly covered by soldermask. While it offers certain advantages, it's essential to consider the potential issues related to copper oxidation and take appropriate precautions.
